Is it possible to add a specific prefab and custom user text in in a multiuser web player?

I am not asking for scripts but general directions in order to evaluate the costs of programming and what sort of programming, web server, middleware are needed.

Here is the situation I want to have an on-line space where users can add comments in specific places, accompanied by a prefab let's say an exclamation mark. so I want to pass a vector and a text string in a server where every other user can read it. And of course save it in some sort of database, xml file or something like that. Preferably it would be great if this was happening immediately. So for example while i am writing a comment here every other person see the comments immediately. an anonymous or not login system might be required. I am not interested in avatars or other networking stuff ...

I am really unaware of networking, on-line programming, web servers and how unity works in the background locally.Apache server doesn't ring a bell for example ... even though i have the impression that it is good stuff for that sort of thing!Are there any security limitations for doing stuff like that ? Known pitfalls? What sort of programmer i need? Does unity provides this functionality ?

Thank in advance